Process for the hydrogenation of branched olefins deriving from the dimerization of isobutene

Abstract

A process is described for the hydrogenation of olefinic streams containing sulfurated compounds, obtained starting from hydrocarbon cuts containing isobutene (by means of selective dimerization), characterized by fractionating said streams in one or more distillation columns and hydrogenating separately the two fractions obtained. The stream at the head, with a minimum content of sulfurated compounds, is hydrogenated with conventional catalysts based on nickel or noble metals (Platinum and/or Palladium), extremely active but also very sensitive to sulfur, whereas the bottom of the column, rich in sulfurated compounds, is treated with bimetallic catalysts (for example Ni/Co and/or Ni/Mo), less active but not deactivated by sulfur.

1. A process for the production of high-octane hydrocarbons, which comprises:
 a) dimerizing isobutene that is present in a C 4  cut of a hydrocarbon stream in a dimerization reactor; 
 b) distilling said hydrocarbon stream containing dimerized isobutene in a first distillation column from whose head C 4  products are recovered and from the bottom of which a C 8 -C 16  mixture is recovered as an effluent; 
 c) distilling said effluent in a second distillation column from whose head pure C 8  olefins with a small quantity of sulfur are recovered and from whose bottom a stream comprising most of the sulfur and concentrated contaminants is obtained; 
 d) hydrogenating the stream containing the C 8  olefins with a nickel or a noble metal based catalyst; 
 e) hydrogenating said stream rich in sulfur over a sulfur resistant catalyst comprising a Ni/Mo and/or a Ni/Co catalyst; and 
 f) optionally combining the two hydrogenation fractions so as to prepare a high-octane component, substantially sulfur-free, for fuels. 
 
     
     
       2. The process according to  claim 1 , wherein the noble metal hydrogenation catalyst of step (d) is a palladium and/or platinum catalyst. 
     
     
       3. The process according to  claim 1 , wherein said head fraction of step (c) ranges in amount from 60 to 90% by weight of the entire hydrocarbon stream containing olefinic cuts that is processed to a fuel component. 
     
     
       4. The process according to  claim 1 , wherein, when the C 4  cut has been produced starting from an FCC or coking charge, said head fraction of step (c) ranges in amount from 60 to 80% by weight of the entire hydrocarbon stream that enters the second distillation column. 
     
     
       5. The process according to  claim 1 , wherein, when the C 4  cut has been produced starting from a charge from Steam-Cracking or the Dehydrogenation of isobutane, said head fraction of step (c) ranges in amount from 70 to 90% by weight of the entire hydrocarbon stream that enters the second distillation column. 
     
     
       6. The process according to  claim 1 , wherein the head, fraction of step (c) is hydrogenated over a nickel or noble metal hydrogenation catalyst at a space velocity (olefin volume over catalyst volume per hour) ranging from 0.1 to 10 h −1 . 
     
     
       7. The process according to  claim 6 , wherein said space velocity ranges from 2 to 4 h −1 . 
     
     
       8. The process according to  claim 1 , wherein the olefinic cut to be hydrogenated consists of C 8 -C 16  olefins, whose C 12  olefins content ranges from 5 to 20% by weight of the C 8 -C 16  olefins, whereas the C 16  olefins content ranges from 0.5 to 2% by weight of the C 8 -C 16  olefins. 
     
     
       9. A process for the production of high-octane hydrocarbons, which comprises:
 a) dimerizing isobutene that is present in a C 4  cut of a hydrocarbon stream in a dimerization reactor; 
 b) distilling said hydrocarbon stream containing dimerized isobutene in a single distillation column from whose head C 4  products are recovered and from whose bottom a C 8 -C 16  mixture containing sulfurated compounds is recovered, and a lateral cut being obtained as a liquid or vapor that is comprised of essentially sulfur free C 8  olefins; 
 c) hydrogenating the stream of the lateral cut containing C 8  olefins over a nickel or noble metal catalyst; 
 d) hydrogenating the stream that is rich in sulfur obtained from the bottom of the distillation column over a sulfur resistant catalyst comprising a Ni/Mo and/or a Ni/Co catalyst; and 
 e) optionally combining the two hydrogenation fractions so as to prepare a high-octane component, substantially sulfur-free, for fuels. 
 
     
     
       10. The process according to  claim 9 , wherein the noble metal hydrogenation catalyst of step (c) is a palladium and/or platinum catalyst. 
     
     
       11. The process according to  claim 9 , wherein said lateral cut ranges in amount from 60 to 90% by weight of the entire hydrocarbon stream containing olefinic cuts that is processed to a fuel component. 
     
     
       12. The process according to  claim 9 , wherein, when the C 4  cut has been produced starting from an FCC or coking charge, the lateral cut of step (b) ranges in amount from 60 to 80% by weight of the entire hydrocarbon stream that enters said single distillation column. 
     
     
       13. The process according to  claim 9 , wherein, when the C 4  cut has been produced starting from a charge from Steam-Cracking or the Dehydrogenation of isobutane, the lateral cut of step (b) ranges in amount from 70 to 90% by weight of the entire hydrocarbon stream that enters said single distillation column. 
     
     
       14. The process according to  claim 9 , wherein said lateral cut comprised of essentially sulfur free C 8  olefins, is hydrogenated over a nickel or noble metal hydrogenation catalyst at a space velocity (olefin volume over catalyst volume per hour) ranging from 0.1 to 10 h −1 . 
     
     
       15. The process according to  claim 14 , wherein said space velocity ranges from 2 to 4 h −1 . 
     
     
       16. The process according to  claim 9 , wherein the olefinic cut to be hydrogenated consists of C 8 -C 16  olefins, whose C 12  olefins content ranges from 5 to 20% by weight of the C 8 -C 16  olefins, whereas the C 16  olefins content ranges from 0.5 to 2% by weight of the C 8 -C 16  olefins.